1. Field of the Invention
The present invention relates to a process for manufacturing potato chips in general and in particular to a dual-stage process for manufacturing potato chips in which, in the first continuous process stage, the potatoes are peeled, sliced, washed, partially fried until the slices have a desired moisture content, then frozen, and stored until ready for use. Alternatively, the potatoes are peeled, sliced, washed, steam or water blanched, partially dried until the slices have a desired moisture content, then frozen, and stored until ready for use. The second stage is also a continuous process for preparing potato chips for commercial use at any one of the plurality of locations. The frozen potato slices are finished fried, salted, and packed for commercial use.
2. Description of Related Art
It is well known in the art to prepare french fry potatoes in two stages; in the first stage, preparing and freezing the french fries and, then in the second stage, frying the french flies to the proper state for the immediate sale and use. For instance, U.S. Pat. No. 3,050,404 discloses a method for preparing frozen french fry potatoes. The frozen potatoes have a high moisture content between about 41% and 54%. In this process, the potatoes are cut into french fry strips, the strips are washed after cutting to remove free starch and then are immersed in cooking fat, having a temperature of approximately 149.degree. C. (300.degree. F.). The strips are held in the fat for the amount of time necessary to decrease their moisture content to a level between 41% and 54%. They are then taken from the fat, drained to allow any excess fat to run off, cooled to room temperature, placed in a moisture-proof package, and then frozen. The strips can be held in a frozen state indefinitely for frying at a later time.
U.S. Pat. No. 5,279,840 discloses a method of making reduced fat deep-fried potatoes. The method includes coating the potato slices with a mixture of ungelatinized amylose and calcium, then blanching, partially drying to obtain only about a 5 to 30% total weight loss, parfrying, freezing, and finish frying the slices. The partially dried pieces are parfried for "from about 15 to 60 seconds at a temperature of about 149.degree. C. (3000.degree. F.) to about 190.degree. C. (375.degree. F.)" and then frozen thereafter.
U.S. Pat. No. 4,590,080 discloses a process for preparing parfried and frozen french flies. Potato strips are blanched, parfried, blast frozen, parfried again, and frozen again. The twice parfried and frozen potatoes all had a moisture content of greater than 43%.
U.S. Pat. No. 4,194,016 discloses a process for preparing precooked fruits and vegetables. The specification teaches that potatoes may be peeled, cut, cooked in water or steamed, heated in dry air "such that no part of the potato tissue is lower than 68% moisture", chilled, thin-sliced, frozen, and then fried in oil.
U.S. Pat. No. 3,649,305 discloses a process for preparing frozen french fry potato segments. Potato strips are dehydrated to lose about 10 to 30%, preferably 20%, of their original weight, blanched, parfried, and frozen. Parfrying is carried out for about 30 to 90 seconds in oil at about 149.degree. C. to about 205.degree. C. (about 300.degree. F. to 400.degree. F.).
U.S. Pat. No. 3,397,993 discloses a process for preparing frozen french fry potatoes. Potato strips are blanched, dehydrated by heated air to about 70-80% of their initial weight, partially fried, and then frozen. A potato strip dried to 70% of its original weight would still contain at least about 50-55% moisture. Following dehydration, "the partially dehydrated strips are immersed in a deep fat fryer for a short period of time, for example from about 15 to about 60 seconds at a fat temperature of from about 149.degree. C. to about 1900.degree. C. (about 300.degree. F. to about 375.degree. F.) during which time the moisture content is still further reduced and during which time the strips are partially fried. The strips are then frozen."
U.S. Pat. No. 3,050,404 discloses a method for preparing a frozen partially cooked french fry potato product. The method comprises parfrying the potato pieces until the moisture content is between 41% and 54%. The patentee states that, "It is not practical to cook to a moisture content level substantially less than 41% since the product, in subsequent finishing, is apt to become excessively firm." The specification teaches that the frozen potato strips can be held frozen indefinitely after which cooking is completed by the consumer.
U.S. Pat. No. 2,983,619 discloses a method of preparing preserved potato products. The method is directed to the preparation of "either small whole potatoes, balls, or cut pieces such as cubes, sticks, slices" and so forth. Thin slices as for potato chips, are not specifically disclosed. Potato pieces are partially cooked, and partially dried to a moisture content of 40-68%. The specification teaches that no part of the potato should have more than 68% or less than 40% moisture prior to freezing.
U.S. Pat. No. 2,597,066 discloses a process for preparing and preserving frozen potatoes, typically for french fries and hash brown products. The patent was reissued as Re. 23,890. Cut potatoes are steamed blanched, partially dehydrated to contain 10-15% less moisture than untreated potatoes, chilled, and frozen. Dehydration is performed with an air cooler and heat is not applied during the dehydration step.
In an article in the Journal of Scientific Food AGRIC, 1994, pages 205-210, entitled "Crisp Quality of Two Potato Varieties: Effects of Dehydration and Rehydration", by Kulkarni et al., potato crisps were prepared. The potatoes were washed thoroughly and hand peeled using stainless steel peelers. An automatic electric slicer was used to slice the potatoes to a uniform thickness of less than 1 mm. Crisps were prepared immediately by dipping the slices for two minutes in a thermostatic fryer using sunflower oil at 180.degree. C. (356.degree. F.). One lot of potatoes was processed into dehydrated slices. The time required to denature the enzymes was determined by a blanching test. The slices made from fresh peeled potatoes were blanched in boiling water for four minutes. The blanched slices were then sulfited in an aqueous solution. The drained slices were dehydrated in a hot air cabinet dryer at 60.degree. C. (140.degree. F.) until the moisture content of the slices fell to less than 10%. The drying ratio and yield of dry product were recorded. The dehydrated slices were stored in high-density polyethylene bags until used. Crisps were prepared by frying the dehydrated slices using the frying conditions mentioned earlier.
The rehydration of dehydrated slices was carried out by soaking the dehydrated slices in water at room temperature and also in boiling water with and without 1-25% salt. The amount of water absorbed by the slices was recorded after intervals of 3, 5, 7, and 10 minutes. The rehydrated slices were fried under the standard conditions. Their quality was compared with that of crisps made from dehydrated slices and fresh slices.
In U.S. Pat. No. 3,660,113 a process is disclosed for producing potato chips in which the potato particles are frozen under such conditions that ice crystals form in the individual cells and rupture the cells due to the increase in size resulting from freezing of the water therein. Thereafter potato particles are thawed in warm water and the cell contents released upon cell rupture and thereafter the particles are fried at a temperature in the range of from about 176.degree. C. to about 190.degree. C. (about 350.degree. F. to about 375.degree. F.).
In U.S. Pat. No. 5,302,410, a process is disclosed for preparing frozen parfried potato strips which remain crisp for an extended period of time after finish frying. In this process, potatoes are cut into strips and blanched and then contacted with an aqueous solution containing a hydrolyzed starched product. After contact with the aqueous solution, the potato strips are parfried and frozen and are prepared for consumption by finish frying.
The strips have a width and a thickness from about 6.35 mm to about 12.7 mm and are several inches in length. After cutting, the strips are washed to remove the surface starch and then the strips are blanched by emersion in hot water in the range from about 87.degree. C. to 115.degree. C. (about 160.degree. F. to 210.degree. F.) for 2 to 15 minutes, or with a temperature range of from about 71.degree. C. (170.degree. F.) to about 88.degree. C. (190.degree. F.) for 4 to 10 minutes being preferred. The crispness and rigidity of the finished fried potato strips are improved by contacting the blanched strips, before parfrying, with an aqueous solution containing a hydrolyzed starch product. After contact with the aqueous solution the potato strips are drained and preferably partially dehydrated to reduce their moisture content. For example the potato strips are subjected to heated air having a temperature in the range of from about 65.degree. C. (150.degree. F.) to about 175.degree. C. (350.degree. F.) for from about 5 to 20 minutes in order to reduce the moisture content of the strips to the point at which the strips have lost about 5% to 25% of their initial weight. The partially dehydrated strips are then parfried by immersing them in a deep fat fryer for a short period of time, for example, 20 to 90 seconds at a fat temperature in the range of from about 162.degree. C. (325.degree. F.) to about 200.degree. C. (390.degree. F.). Parfrying removes additional moisture from the strips so that upon completion of parfrying, the potato strips have solids content of between 30% 40% which is equivalent to approximately 60%-70% moisture. After parfrying, the potato strips are frozen, packaged, and shipped or stored for subsequent use. To prepare the parfried strips for consumption, they are finish fried in deep fat or oil bath at a temperature in the range of from about 150.degree. C. (300.degree. F.) to about 190.degree. C. (375.degree. F.) for 1.5 to 3.5 minutes to develop color and crispness.
In U.S. Pat. No. 5,206,048, the raw potato slice, after being washed, is dipped in a chemical solution for 3 to 5 minutes and is then rapidly frozen at-40.degree. C. (-40.degree. F.) for 5 to 30 minutes. Thus, the raw potato slices used in this process are chemically treated before being frozen. The raw potato slice is then stored at approximately -20.degree. C. (-4.degree. F.) and, in the second stage, is then thawed at 30.degree. C. to 80.degree. C. (86.degree. F. to 176.degree. F.). The potato chip is then prepared by frying the potato at 170.degree. C. to 190.degree. C. (338.degree. F. to 374.degree. F.) for 1.5 minutes.
In U.S. Pat. No. 3,660,113, the potatoes are simply peeled, washed, sliced, and are then frozen raw. Immediately after freezing, the frozen slices were immersed in warm water at a temperature between about 32.degree. C. and about 49.degree. C. (90.degree. F. and 120.degree. F.) for from 1 to 3 minutes sufficient to thaw the potatoes. After thawing, the slices were then fried. Thus, the disclosure does not concern itself with preparing potatoes for long-term storage before being prepared for commercial use.
U.S. Pat. No. 4,254,153 concerns a two-stage potato processing system which requires two drying steps and a blanching step--the product is then parfried and frozen.
In U.S. Pat. No. 4,632,838 also relates to a two-stage potato chip process in which there is a chemical treatment of the potato slices, then blanching, then a drying step, and then two parfry steps before freezing.
In U.S. Pat. No. 4,761,294, concerning a two-stage potato chip process, the potato slices are water blanched, dried, parfried, frozen once, then subjected to hot air impingement for six minutes and then frozen a second time.
In U.S. Pat. No. 4,900,576, a two-stage potato process is disclosed in which there is a blanching of the potato particles, a chemical treatment of the potato slices, two parfry steps, and two freeze steps. The first parfry occurs before the first freeze, which is a quick freeze, then the particles are thawed, parfried the second time, and then given a final quick freeze.
Currently, potato chips are generally produced in a one-step frying process by frying slices (approximately 80% moisture) to a moisture content of less than 2%. The frying process can be continuous or batch. For a commercial process carried out at a number of locations, this involves transporting raw potatoes, sometimes over long distances, from the locations where they are grown to the sites where the potato chips are made. At each site, a number of processing steps are involved and they are: potato storage, potato washing, peeling, paring and trimming, slicing, washing, and frying to a specific finished product moisture. The potato chips are then salted and bagged and delivered to commercial locations for sale. At each of the different locations, all of the processing steps are basically duplicated to produce commercially available potato chips.
Those potato products that are prepared by a two-stage process are chemically treated and have two or more freezing steps or two or more frying steps in the first stage of the process. It is clear from the cited references that there is no commercially acceptable process existing for forming or producing frozen potato chips that can subsequently be fried for commercial use. All of the references relating to french fry potatoes use potato segments that are quite thick and wide and that have a large moisture content when frozen and eventually when fried also contain high moisture content.
It would be ideal to have a commercially viable process for producing potato chips, in two stages, that does not involve chemicals, either pre- or post-treatment. The initial stage would be continuous and would include washing, peeling, paring and trimming, slicing, washing, reducing the chips to a specific half-product moisture, and then freezing the product. The frozen product can then be stored in a cold warehouse for extended periods of time, up to several months. In the second stage, which would also be continuous, the frozen product is finish fried to a required moisture level, seasoned and bagged for distribution. With such a system, a large central location could be situated near the potato fields and utilized to produce an initial half-product that is stored for later distribution to a number of finishing plants. The potential advantages of such a process are in reduced freight costs of potatoes, reduced water and sewage costs, ability to convert waste products into high value by-products, and to provide consistent feedstock to the finishing fryer to produce high-quality finished products all year round. In addition, the expensive equipment used during the first stage could be located at one site near the potato source. The second stage apparatus is less expensive and can be situated at a number of sites where the finished chips are fried, salted, and bagged for distribution to commercial sources. Thus, equipment costs would be substantially reduced.